Enhanced performance and reduced emissions of regulated pollutants and (nitrated) polycyclic aromatic hydrocarbons using CeO2 and CuO–CeO2 nanoparticle diesel additives

This study investigates the effects of cerium oxide (CeO 2 ) and copper-modified cerium oxide (CuO–CeO 2 ) nanoparticles as diesel fuel additives under varying engine loads and doping concentrations (50 and 100 ppm). Emphasis is placed on combustion behavior, pollutant emissions, and the distribution and toxicity of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs (NPAHs). Results show that nanoparticle addition significantly enhances combustion. The heat release rate (HRR) increases by 7.17–9.44%, cylinder temperature rises by 0.84–3.19%, and indicated specific fuel consumption (ISFC) decreases by 5.88–8.43%. CeO 2 facilitates NO reduction and CO oxidation through its redox activity and oxygen storage capacity, while CuO–CeO 2 achieves superior emission control at low concentration, reducing CO and NO x by 32.2% and 7.56% via a synergistic catalytic effect. Although total PAHs show a slight increase, a pronounced particulate-to-gas-phase shift is observed, especially under CuO–CeO 2 , where the solid-to-gas conversion rises by 34.4–78.3% compared with diesel. Compositional analysis reveals a marked increase in naphthalene (79.3–531%) and a decline in medium- and high-ring PAHs, likely from catalytic oxidation or desorption of low-ring PAHs suppressing soot. In parallel, NPAHs decrease significantly, suggesting inhibition of nitration pathways during combustion. Despite higher total PAHs, the toxic equivalency (TEQ) under CuO–CeO 2 decreases up to 32.5%, indicating a lower toxicity burden. Collectively, these results show that functional metal oxide nanoparticles enhance diesel combustion efficiency, reduce gaseous pollutants, and alter PAH/NPAH formation in a way that mitigates toxicity, supporting their potential as sustainable emission control additives for advanced engines.